Breast cancer is the most common malignancy affecting women in the US, and the second leading cause of cancer death. We have participated in several National Surgical Adjuvant Breast Project (NSABP) studies. These multi-institutional investigations have examined both prevention (Tamoxifen P-1 Trial) and treatment of breast cancer. The early results of this study demonstrated a decrease in the incidence of breast cancer of 45% in the group of patients who received tamoxifen. The study results were reported, but not yet published. All participants were informed and are still being followed. The NSABP has not decided how many years these patients will be followed.